Organometallics 1993,12, 2414-2416
2414
Insertion Reactions of Isocyanides and Nitriles into Unsupported Iron-Aryl Bonds: The Synthesis of a Dimeric Iron(11) Homoleptic Iminoacyl Complex Alain Klose, Euro Solari, Richard Ferguson, and Carlo Floriani' Section de Chimie, Universiti? de Lausanne, Place du Chateau 3, CH-1005 Lausanne, Switzerland
Angiola Chiesi-Villa and Corrado Rizzoli Istituto di Strutturistica Chimica, Centro di Studio per la Strutturistica Diffrattometrica del CNR, Universitd di Parma, I-43100 Parma, Italy Received April 1, 1993 Summary: The reaction of the dimer FezMesr [Mes = 2,4,6-Me&HJ (1)with ButNC led to [Fed($-C(Mes)NBu')}2(p-C(Mes)=NBut)J (a,a thermally stable homoleptic dimeric iminoacyl derivative containing both a terminal and a bridging iminoacyl functionality. 2 has a very short Fe-Fe distance [2.366(2) A] and a low magnetic moment C3.40 p~ per iron at 250 K ] . A 2-fold insertion was observed in the reaction of 1 with PhCN to in give dimer 3, [((PhCN)(Mes)Fe}z(p-N=CPhMes}J, which the iron atoms are bridged at a distance of 2.860(2) A from each other by two imino anions. Complex 3 has amagneticmoment o f 2 . 8 2 p ~ a t 2 5 0 K suggestingastrong ~ magnetic coupling between the two iron atoms. The iron-carbon u bond is among the most widely used organometallic functionalities in both stoichiometric and catalytic pr0cesses.l The variety of Fe-C bond containing derivatives employed derives both from the variety of ancillary ligandsused and from the different functionalities on the alkyl or aryl group (we note, for example, the important role played by the iron-acyl fragment and ita derivatives2). Homoleptic alkyl and aryl derivatives of iron, functionalized or not, are rare, normally poorly characterized,and thermally unstable? Additionally,their chemistry is practically unknown; in this context, ironmesityl represents a rare example of a usable homoleptic iron(11). Iron-mesityl was synthesized several years agora and its structure, [(Mes)Fe(p-Mes)zFe(Mes)l[Mes = 2,4,6Me~CgI21,1,has been very recently elucidated." Complex
* To whom correspondence should be addreseed.
(1) (a) Peareon, A. J. In Advances in Metal-Organic Chemistry; JAI Press: London, U.K., 1989; Vol. 1, pp 1-35. (b) Davies, S. G. Organotransition Metal Chemistry; Applications to Organic Synthesis; Pergamon: New York, 1986. (c) Pearson, A. J. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982;Vol. 8, Chapter 58. (d) The Organic Chemistry oflron;Koerner von Gustorf, E. A., Grevels, F. W., Fiachler, I., Eds.; Academic: Orlando, FL, 1978, 1981; Vols. I and 11. See also earlier reviews cited in these articles. (e) Reetz, M. T.; Stanchev, S.J. Chem. Soc., Chem. Commun. 1993,328. (2) (a) Liebeskind, L. S.; Welker, M. E.; Fengl, R. W. J. Am. Chem. SOC.1986,108,6328. (b) Davies, S. G. Pure Appl. Chem. 1988,60,13. Davies, S . G . Chem. Br. 1989, 268. (3) (a) Eisen-Organische Verbindungen (Organic Iron Compounds). Gmelin Handbook of Inorganic Chemistry; 1976; Vol. 36, Part B, pp 6-15. (b) Davison, P. J.; Lappert, M. F.; Pearce, R. Chem. Rev. 1976,76, 219. (c) Johnson, M. D. Mononuclear Iron Compounds with 71Hydrocarbon Ligands. In Comprehensive Organometallic Chemistry; Wilkinaon, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 4, Chapter 31.2. (4)(a) Machelett, B. 2. Chem. 1976,16, 116. (b) Muller, H.; Seidel, W.; Gbrle, H. J. Organomet. Chem. 1993,445, 133.
0276-7333/93/2312-2414$04.00/0
1offers the unique opportunity to study the organometallic chemistry of the Fe-C bond in the absence of an ancillary ligand. We report here a preliminary account of an extended investigation we are doing on the insertion reactions into the iron-carbon bond. This is one of the major reactions of iron organometallic derivatives in stoichiometricor catalytictransformations.l*&Specialcare should be taken for the synthesis and storage of 1, which is very air and heat sensitive. We report here a revised, large scale synthesis of 1.6 The reaction of 1with ButNC led to the first homoleptic iminoacyl of iron(I1). The reaction is carried out a t 0 "C in THF and then at room temperaturee6 Complex 2 was
isolated as a black crystalline solid. Ita thermal stability both in solution and in the solid state is much higher than that of 1. A large and strong band centered at 1601cm-l can be assigned to the iminoacyl groups. Compound 2 contains v2-C,N and p&,N iminoacyls, according to the structure reported in Figure lA.7 The structure consists of dimers having a CZcrystallographic symmetry. The six-membered dimetallic ring has a boat (5) Procedure for 1: Freshly prepared crystallineFeCl2.1.6THFTHF(20.70 g, 88.2 m o l ) wae suspended in a mixture of THF (500 mL) and dioxaue (100 mL). The suspension wan cooled to -30 OC and then reacted with MesMgBr (1.206 M, 147 mL, 177 "01) with stirring and occasional shaking. The temperature wan raised to room temperature and the suspension stirred for 2 h. The magneeium salta were filtered out and the fdtrate evaporated to dryness. The solid wae dried under vacuum before dieeolving in EhO (500 mL). A second fiitration wan performed to eliminate the h t traces 9f magneeium nalta. Evaporating EhO to 100 mL yielded a deep orangered crystalline solid, FepMw (52%). The yield hae not been optimized. Anal. Calcd for C m e : C, 73.48; H, 7.54. Found C, 73.20; H, 7.62. The magnetic moment independent of the temperature is 1.71 p~ per iron in the range XI-250 K. It can be affected by thermal decompositionof 1and ie significantly different from that reported in refs 4a and 4b. (6) Procedure for 2 A THF (100 mL) solution of ButNC (3.30 mL, 39.4 "01) waa dropwise added to a THF (200 d) solution of 1 (6.80 g, 19.7Ommol)atO0C. Theeolutionwaethenetirredatroomtemperature overnight and turned black. It ~ B L evaporated I to drynegs and the residue dissolved in n - h e m e (200 mL). Partial evaporation of the eolvent gave 2 (48.6%)an black cryatale. Anal. Calcd for C a P e a : C, 73.03; H, 8.76; N, 6.08. Found C, 72.40; H, 8.80, N, 6.45. IR: u(C==N)(Nujol) WE band at 1601 cm-l. p 3.27 BB at 80 K and 3.40 p~ at 250 K.
-
0 1993 American Chemical Society
Communications
Organometallics, Vol. 12, No. 7, 1993 2415 [113.0(5)01and Fel’-N2-C10 [97.6(4)OI bond angles, are consistent with a possible metal-metal interaction.8 The formation of iron iminoacyl either from migratory insertion of an alkyl into an isocyanideg or from other reactionslO is well-known. The resulting iminoacyl is commonly $-bonded to a single metal center:JO while some rare examples are known in which the iminoacyl acta as a p&,N bridging ligand.lW The homoleptic iminoacyl2 maintains a reactive metal-carbon bond, which we are currently exploring. Homoleptic organometallic derivatives containing a-functional groups are rare for the middle and late transition metals. By contrast, this is not the case for early transition metals.l1J2 The reaction of 1with benzonitrile not only sheds light on the possible mechanism of insertion reactions with 1 but also suggests how a mixed ligand insertion derived complex can be obtained when the appropriate sequence of inserting substrates is used.
c;
Me
2u(n1 collected at room temperature (5 < 28 < 50°) and corrected for absorption, the final R value was 0.058 (R, = 0.062).
The nature of complex 3 suggests that (i) the migratory insertion of the mesityl to the substrate is preceded by the precoordination of the substrate with the iron changing from three- to four-coordinate; (ii) the bridging mesityl group migrates first, while the less reactive terminal mesityl then migrates to the isonitrile in reaction 1,but does not migrate to the less reactive coordinated benzonitrile in reaction 2. Reaction 213 was carried out in toluene at -30 “C, and then the temperature was raised to room temperature. The violet solid was recrystallized from benzene. Regardless of the reaction conditions and the stoichiometry, a single insertion of two benzonitriles was observed, leading to two briding diarylimino groups (Y-N, 1602-1613 cm-I), while two other benzonitriles (u-N, 2229 cm-l) are coordinated, one to each iron. The ORTEP diagram of (8)Fehlhammer, W. P.; Stolzenberg, H. Dinuclear Iron Compounds with Hydrocarbon Ligands. In Comprehensive Organometallic Chemistry;Wilkinson, G., Stone,F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 4, Chapter 31.4. (9) (a) Bellachioma, G.; Cardaci, G.; Macchioni, A,; Reichenbach, G. Inorg. Chem. 1992, 31, 63 and references therein. (b) Cardaci, G.; Bellachioma, G.; Zanazzi, P. Polyhedron 1983,2,967. (10) (a) Fehlhammer, W. P.; Hirschmann, P.; Mayr, A. J. Organomet. Chem. 1982, 224, 153. (b) Brunner, H.; Kerkien, G.; Wachter, J. J. Organomet. Chem. 1982,224, 295. (c) Adams, R. D.; Chodosh, D. F.; Gobmbeski, N. M.; Weissman,E. C. J. Organomet. Chem. 1979,172,251. (d) Seyferth, D.; Hoke, J. B. Organometallics 1988,7,524and references therein. (11) Durfee, L. D.; Rothwell, I. P. Chem. Reu. 1988,88, 1059. (12) Vivanco, M.; Ruiz, J.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Organometallics 1990,9,2185. Rub,J.; Vivanco, M.; Floriani, C.; ChiesiVilla, A,; Guastini, C. J. Chem. SOC.,Chem. Commun. 1991,214. Ruiz, J.; Vivanco, M.; Floriani, C.; Chiesi-Villa,A.; Rizzoli, C. Organometallics, in press. (13) Procedure for 3: A toluene (100 mL) solution of benzonitrile (2.70 g, 26.70 11111101)was dropwiee added to a toluene (150 mL) solution of 1 (3.90 g, 13.30 mmol) at -30 OC. The solution was stirred at room temperature ovemight and turned violet and was then concentrated to 100 mL. A violet crystalline solid was obtained (54.6%),which was recrystallized from benzene. Anal. Calcd for C a f i e l : C, 76.80; H, 6.44; N, 5.60. Found C, 76.83; H, 6.81; N, 5.82. I R v(C==N)(Nujol) 1602-1613 cm-1; v(C=N) (Nujol) 2229 cm-1. p = 1.42 p~ at 80 K and 2.82 pg at 250 K.
2416 Organometallics, Vol. 12, No. 7, 1993
w
Communications N2,Fel',N2/~Fel,Cll,Nl]is90.1(2)O. The Fel-C11 bond distance [2.119(5) AI is significantly longer than that in 1 [2.023(5) and very close to that which we observed in the tricoordinate iron metalate [Fe(Mes)J- [2.117(6) The Fe-aFe distance [2.860(2) AI in 3 is much longer than that in complex 2, even though the two iron(11)atoms are bridged by a single donor atom. The iron-iron distances in complexes 2 and 3 fall respectively in the upper and lower range of a large variety of dinuclear iron complexes.8 The magnetic properties of 2 and 3 deserve special comment. In both cases the F e F e distance and the nature of the bridging ligand facilitate a significant magnetic coupling between the two iron(I1) atoms: complex 2 has a p of 3.27 p~ at 80 K and 3.40 p.1~at 250 K, while complex 3 has a p of 1.42 p~ at 80 K and 2.82 p~ at 250 K. We should emphasize that the degree of magnetic coupling is inversely related to the Fe-Fe distance. This supports the idea that the bridging ligand is probably a major factor in the coupling between the two d6 centers.
C24
C23
Figure 2. ORTEP view of complex 3 (30% probability ellipsoids). Selected bond distances (A) and angles (deg)are as follows: Fel-Fel' = 2.860(2),Fel-N1 = 2.090(5),Fel-N2 = 2.014(5), Fel-N2/ = 2.043(5),Fel-Cll = 2.119(5), Nl-C7 1.142(9), N2-C27 = 1.288(7), C27-C31 1.524(8), C27C21= 1.493(7);Nl-Fel-N2 = 101.8(2),Nl-Fel-N2' = 101.5(2),Nl-Fel-Cll= 114,1(2),N2-Fel-N2' = 90.4(2),N2-FelC11 = 122.4(2), N2'-Fel-C11 = 122.1(2), Fel-Nl-C7 = 171.0(6),Fel-N2-Fel' = 89.6(2), FelCN2-C27 = 126.6(5), Fel-N2-C27 = 143.6(5),N 2 4 2 7 4 2 1 = 123.8(5),N2-C27C31 = 120.1(5),C21-C27-C31 = 116.1(5). Primes denote a transformation of -z, -y, -2. 3 is shown in Figure 2, with a selection of structural parameters.14 The dimer has a center of gravity on a crystallographic center of symmetry a t (O,O,O). The two irons are bonded to the terminal ligands Mes and PhCN in a normal fashion and they are bridged by a diary1imino group. The FezNz skeleton has a perfectly planar geometry, in a kind of aza-iron-cyclobutadiene structure. The dihedral angle between this plane and the plane containing the other two donor atoms around iron [Fel,-
Acknowledgment. We thank the Fonds National Suisse de la Recherche Scientifique (Grant. No. 20-3342092) for financial support. Supplementary Material Available: Tables of crystal data (SI), atomic coordinates (SII-SV), thermal parameters (SVI, SVII),and bond distancesand angles (SVIII, SIX)for complexes 2 and 3 (11pages). Ordering informationis given on any current masthead page. OM9302094 (14) etructure of 3. C egNc2C ,M,= 1157.2, triclinic, space group p1,a = 12.680i3) f l 1 3 . 5 1 0 ( 3 2 , c = 10.870(5)A, a = 107.63(2)',@= 104.30(3)',r =67.OO(2)', V p 1615.9(10)A*,Z= 1 , p e 1.189 g cm-3;X(Mo Ka) = 0.710 69 A, ~ ( M Ka) o = 4.91 cm-1; crystal dunensions 0.18X0.22 X0.35". Thestructurewassolvedasfor1. Therefinement was carried out anisotropically for all non-Hatom. The hydrogen a t o m were located by difference methode and introduced into the final refinementas fiied contributore(Vb= O.OSA*). For 2806unique observed reflections [I > 2u(Z)I collectad at room temperature (5 < 28 < 50') and correctedfor absorption,the fiinalR value was 0.059 (R,= 0.063). During the refinement, all the eromatic rings were constrained to be regular hexagons (C-C, 1.395 A). All calculations were carried out with the we of SHELX-76. (15) Unpublished results.
